The present invention relates to programmable Read-Only-Memory (ROM). More specifically, the present invention uses a multiplexor and n-bit subfunction encoder to achieve a high-speed, ultra-dense, via contact programmable ROM.
A common goal in designing and manufacturing integrated circuits (ICs) is to reduce the size of each IC. Generally, a smaller IC provides several advantages. First, by consuming less space on a wafer, more circuits are produced for the same cost as for a larger IC. Second, a smaller IC will likely operate faster as the signals have less distance to travel on the surface of the IC. In some cases, this may result in lower power consumption by the IC.
There are different ways to reduce the size of an IC. The relative size and spacing of circuits can be reduced. Conventionally, engineers are attempting to manufacture ICs using sub-micron device geometries. Other ways include improved placement of individual circuits on an IC. Such intelligent place and route techniques will reduce the area consumed by interconnect traces.
Still other ways to reduce the size of a digital circuit is to use circuit reduction design techniques such as Karnaugh maps (so-called K-Maps) and Boolean algebra to simplify the common circuits. However, even though this method is a necessary first step that must be performed, it cannot meet today demand to miniaturize the IC circuits. Another method is to use Very Large Scale Integrated Circuit (VLSI) design to add more transistors into a given silicon area. Today""s technology can add ten of million of transistors into a given silicon area. However, this VLSI method has its problems and constraints. When transistors and active circuits are packed close together, the heat dissipation and cross talk signals may cause the neighboring transistors to malfunction. Especially when today""s technology demands a very fast speed, for example up to the 400 MHz range. There exists a need to find new methods to reduce IC size in sub-micron dimension to meet the demands for ultra-dense and high-speed IC circuitry.
The present invention in its preferred embodiment represents a high-speed, ultra-dense logic circuit using a contact programmable read-only-memory (ROM) which is controlled using a multiplexor cell technology. According to the invention, high density is achieved by fully encoding n-bits of address space and programming the core with 2n bits of information per contact through the use of higher order logic techniques. Through the use of these subfunctions a circuit can realize a relatively large reduction in area on an IC for implementing a circuit.
A MUX-based ROM uses n-bit subfunction encoding to implement a logic function. A ROM is programmed for selecting one of a plurality of subfunctions. A MUX is coupled to receive an input. The MUX is also coupled to the ROM for selecting subfunction in response to the input. A ROM output provides a signal responsive to the subfunction.
The nature, principle and utility of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.